Confirming the happy news on Twitter with a cute picture of her older daughter Aaliyah holding her little brother's hand, Katherine revealed his unusual - and very long - name.

"Andrew, Aaliyah and I are proud to announce the arrival of our gorgeous son Xander Robert Selwyn Levitas," he wrote.

"His middle names honour our late fathers who live on in our little ‘Defender of Men’ (Meaning of Xander).

How Katherine announced the arrival of her newborn son

Katherine already has two-year-old daughter Aaliyah (Image: Getty)

Our family, our home and are hearts could not be more full of love & we are incredibly grateful for the gift of being parents to these beautiful children.

"Cwtches to you all xxx," she added.

Opera singer Katherine announced her pregnancy in mid-November 2017 with a cute Instagram post featuring their two-year-old daughter Aaliyah Reign wearing a cape and with the slogan 'Sidekick coming soon...'.

The cute post that announced Katherine and Andrew were expecting again (Image: Instagram)

The opera star at the 2016 Pride Of Britain awards (Image: Getty)

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She told her fans: "Andrew and I are overjoyed that our family will be growing in 2018 with the addition of our second child - a baby brother for our little superhero Aaliyah!!!"

In 2016 the chart-topping star, 37, revealed her plans to expand their family, explaining: "We definitely want another child.

"There's no ovulation charts on the wall or anything . . . not yet anyway . . . but that's because I'm about to go on tour.